Hydrogenation of nitriles



United States Patent M 3,117,162 HYDRGGENATION 0F NRTRILES Paul N. Rylander, Newark, and Jay G. Kaplan, Irvington, N.J., assignors, by mesne assignments, to Engelhard Industries, Inc., Newark, N.J., a corporation of Delaware No Drawing. Filed" Mar. 30, 1960, Ser. No. 18,516 2 Claims. (Cl. 260-583) This invention relates to hydrogenation of nitriles in the presence of certain platinum metal catalysts with minimization of the coupling reaction generally tound to occur in the reduction of nitriles. More particularly, it refers to such hydrogenations of aliphatic nitriles with catalysts containing rhodium or ruthenium, and such hydrogenations of aromatic nitriles with catalyst containing rhodium or palladium.

It is known that nitriles can be catalytically reduced to amines, and a variety of catalysts have been employed for this purpose. The normal product of the reaction of a nitrile should be a primary amine,

but very frequently coupling reactions leading to secondary amines 2RCEN+4H (RCH NH+NH or tertiary amines predominate 3RCEN+ 6H (RCH N+2NH The extent of the coupling reaction is mainly dependent upon the catalyst used. It is afiected to some extent by the temperature and pressure of the reduction reaction, concentration of the substrate, the use of a solvent, the amount of catalyst present, and the structure of the nitrile which is reduced.

Coupling reactions are generally undesirable and wasteful of the substrate; hence many means have been employed to minimize :coupling, including reduction in a very dilute solution, and the use of organic anhydrides or liquid ammonia as solvents.

The preferred reaction pressure Where rhodium is used to reduce aliphatic nitriles is in the range of about 1 to 50 atmospheres, whereas for the reduction of aliphatic nitriles using ruthenium as a catalyst, reaction pressure is generally in the range of about 10 to 300 atmospheres. For reduction of aromatic nitn'les with either rhodium or palladium as a catalyst, the preferred reaction pressure is in the range of about 1 to 50 atmospheres.

The reaction may be conducted in the presence or the absence of a solvent, and where a solvent is employed, it should be one which does not poison the catalyst. Suitable solvents are benzene, acetic acid, butyl alcohol, hexane and the like. The solvent may be present in a ratio of 1 to 99 percent by weight of the substrate. The catalytic metals, i.e. rhodium, palladium, or ruthenium may be used in the form of their blacks. Preferably, they are supported on carriers such as, for example, carbon, alumina, including activated alumina, silica, including kieselguhr and synthetic gel, titanium dioxide, calcium carbonate, barium sulfate, bentonite and the like. The preferred supported catalysts include a catalytic metal content in the range of about 0.1 to 10 percent by weight of the total catalyst, but catalysts having a higher metal content can be used if desired.

The method of preparation of the catalyst will vary 3,117,152 Patented Jan. 7, 1954 depending upon the type of process in which it is to be employed. When the precious metal is dispersed throughout a' macro-size support or is present with the support in a powder form, it is customary to co-precipitate it with the support, or to use various impregnation methods. For example, aluminum hydrate and rhodium sulfide may be co-precipitated by adding a solution of ammonium hydroxide and ammonium sulfide to a solution of alumi num chloride and a soluble compound of rhodium. The resulting precipitate is then washed free of chloride, dried and calcined to produce an active catalyst. Alternatively, a finely divided catalyst support, or support precursor, may be mixed with water and impregnated with an aqueous solution of a precious metal salt. The precious metal may be fixed on the support as such, or as an insoluble sulfide prior to drying. In the case of a carbon support, it is usually unnecessary to calcine the catalyst, while in the case of an inorganic support such as an oxide hydrate, it is generally beneficial to calcine it prior to use. This calcination is most conveniently effected in air.

In the case of macro-size catalysts for use in fixed bed or moving bed reactors, it is often desirable to have the catalytic metal dispersed on the external surface of the particles. In the case of an adsorbent support, this is most readily accomplished by soaking the support in an aqueous solution of a precious metal salt. The catalyst is then dried and activated by air calcination. For example, fihinch activated alumina tablets may be soaked in a solution of a soluble salt :of rhodium so as to provide 0.5 percent rhodium on an alumina base. The rhodium salt is adsorbed on the external surface of the particles, after which the particles are dried at a temperature of 120 C. and calcined for two hours at a temperature of 480 C. to provide an active catalyst.

Catalysts for use in fluidized beds or slurry systems are provided as fine powders, usually having a particle size in the range of about 5 to microns. Catalysts for fixed bed or moving bed processes are provided as macro size particles, usually from to %-inch in diameter, and having a length approximately equal to the diameter. In the latter case, the particles may be formed by a tabletting or extrusion operation prior to or after impregnation with the catalytic metal.

It is usually preferable to prereduce ruthenium catalysts in a hydrogen atmosphere prior to use.

The process of the present invention may be conducted in either the liquid or vapor phase and, where the vapor phase is employed, the space velocity may be in the range of about 0.1 to 50 standard volumes of gas per volume of catalyst per hour, preferably 0.5 to 10 standard volumes per volume per hour.

The concentration of catalyst relative to material to be hydrogenated, in liquid phase operation, may be in the range of 0.01 to 20 grams of the compound to be hydrogenated per gram of catalyst, preferably 0.5 to 5 grams per gram.

The reaction temperature for liquid phase reactions may be in the range of 0 to 250 C., and for vapor phase reactions, from about 100 to 400 C.

A study was made using propionitrile to ascertain the effect of concentration on product distribution. Propionitrile in 4.4 volume percent, 8.4 volume percent, 15.5 volume percent and 26.8 volume percent in hexane Was hydrogenated, using 300 mg. of 5 percent rhodium on carbon catalyst, at a temperature of 25 C. and a pressure of 50 p.s.i.g. The most dilute solution favored primary 3 amine formation, but the secondary amine generally predominated. At other concentrations, all the amine is secondary. Generally speaking, substrate concentration does not have a significant eiiect upon product distribution.

A study was made of the effect of catalyst concentration on the distribution of amine in the hydrogenation of propionitrile, using :a 5 percent rhodium on carbon catalyst. There was :a small amount of primary amine formed, using small amounts of catalyst but, otherwise, distribution was virtually independent of the amount of catalyst present, indicating that coupling occurs primarily on the catalyst surface.

Another study was made of the effect of mixing the catalyst on the distribution of amines. Platinmn poisoned easily, and 300 mg. of 5 percentp-latinum .on carbon was generally insufficient to completely hydrogenate the nitrile. When the reactor was opened and more platinum on carbon catalyst was added, the reaction continued further. However, tertiary amine was theonly amine found in these two experiments. It 5 percent rhodium on carbon catalyst is added to the spent platinum catalyst, which has become inactive due to poisoning, the reaction continues to completion, but the product is solely'tertiary amine instead of containing a substantial amount of secondary amine which the rhodium catalyst should yield.

Another study was made of the effect of excess product on the direction taken in the hydrogenation of propionitrile. It was observed that primary amine poisoned the catalyst where-as the use of secondary amine as a solvent promoted the formation of tertiary amine. No primary or secondary amine formed when tertiary FZlIIliIlC was used as a solvent; presumably tertiary amine is formed, but it could not be measured. I-t appears that the use of an amine solvent does not promote the formation of primary amine.

The invention will be funther illustrated by reference to the following specific examples: 1

EXAMPLE I A study was made of the hydrogenation of propionitrile at room temperature and atmospheric pressure, using various platinum metals catalysts. In each of these tests, 300 mg. of catalyst were placed in a one-liter heavy wall Erlenmeyer flask, together with 50 mi. of hexane containing 0.1 mole of propioni-trile. The flask was placed in a shaker, capped and repeatedly evacuated and filled with hydrogen gas. The system was then connected to a gas burette and leveling bulb containing water, in order to measure hydrogen uptake. The shaker was started and the hydrogen reacted was measured on the gas burette at various intervals of time.

Results of these tests ,are shown in Table I below.

It can be readily seen from the tablethat, under conditions in which palladium and platinum give exclusively tripropyl amine, rhodium gives predominately dipropyl amine, thus demonstrating that rhodium I as an unexpectedly small tendency to promote coupling. The peroentages in the table express the percentage of each amine 5 as a total of all the primary amines. t

Table I .Hydr0genatz0n of Propyl Nztrlle m Hexane at 25 C.

Distribution of Amino Ml. l-nl Catalyst min. per

Percent Percent Percent 300 mg. Propyl Dipropyl Tripropyl of cat.

amine amine amine 5% Pd as PdO on Mg silicate. 0 0 5% Pd on Mg silicate 0 0 5% Pt on carbon (Norii: A)-.- 0 0 5% Pd as PdO on carbon (Nor-it Sg Ex) 0 0 5% Pd on acid leached carbon (Norit F) 0 0 100 5% Pton carbon (N orit Sg .Ex 0 o 100 5% Pd on carbon (Norit Sg E 0 0 100 1.0 5% Pd on carbon (Darco 0 0 100 1. 5 2.5% Pd, 2.5% Ru on carbon (Norit) 0 31 69 3.7 0.5% Rh on A1303 p0wdcr 90 6 1.0% Rh on A1203 powder 0 100 0 8.1 2.0%.Rh onAlzOa powder. 0.5 90 0 4 5.0% Rh on carbon (Darco G-60) 4. 5 95, 5 0 4. 6 Rh on carbon (Norit 16 84 0 10 5% Rh on carbon (Norit)- 0 100 O 11 5% Rh on asbestos l 0 100 0 1. 2 30 5% an on CaCOa 90 4 EXAMPLE 2 measured by the drop in pressure.

of .propionitrile.

Results are shown in Table 11 below.

In no case do the percentages of amine found add to percent. This is attributed tothe formation of intermediates, such as I IH NHQ which have no absorbance at 6.20, 8.83 or 8.40,:4.

Table II.Hydr0genatiorz of Propz'onitrile EFFECT OF METAL AND PRESSURE ON PRODUCT DISTRIBUTION 5O p.s.i.g. 500 p.s.i.g. 1000 p.s.i.g. Catalyst Compound v V Conv. Yield Conv. Yield Conv. Yield (percent) (percent) (percent) (percent) (percent) (percent) 5 Rh C--- 100 100 I 0 0 0 '0 92 92 94 94 .2 0 2 0 5 PG C--- 7 I 1 0 0 0 0 0 0 0 0 5 Pt C 3 I 1 0. O 0 0 O 0 0 0 0 0 21 16 38 13. 61 5% Ru/C--- 0 100 .100 l 0 0 21-37 21-37 10-18 10-1 2 Amine- 0' 0 24 24 34 3 3 Amine--. 0 0 0 EXAMPLE 3 Results are shown in Table IV below.

These results show that carbon tetrachloride, chloroy Was {made of the effect of Emperafilfe on form, dioxane and pyridine poisoned the cataylst. The mbutlon of 311111168 Iesulting from the hydrogenation of other four solvents, namely, benzene, acetic acid, butyl propionitrile. Conditions used were 50 p.s.i.g. with the l hol and h xane, gave approximately the same amine reaction being conducted in the shaking bomb previously distribution; none gave a good yield of primary amine. described. 0.1 mole propionitrile in 50 ml. hexane was Analysis was by infrared absorption. Some solvents inreacted with hydrogen over 300 mg. of powdered catalyst terfered with the amine absorption bonds; in the table in each case. they are indicated as blocked out.

Table I V.Efiect of Distribution Using Various Solvents With 300 mg. of 5 Percent Rh on Carbon at 5'0 p.s.i.g.

Nitrile Primary amine Secondary amine Tertiary amine Solvent Conv. Yield Conv. Yield Conv. Yield Conv. Yield (percent) (p rcent) (percent) (percent) (percent) (percent) (percent) (percent) Carbon tetachloride O 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 O 0 O 41 Weak Weak Present Present 0 0 0 0 Present Present 0 0 Butyl alcohol 35 Weak Weak Hexane 100 3 3 89 89 0 O 1 Incomplete. 2 Blocked out.

EXAMPLE 5 Results are shown in Table III below. In the range of C. to 150 C., it was not observed A study was made of the hydrogenation of benzonitrile that temperature had a marked effect on distribution. The at various pressures. In the p.s.i.g. study the shaking trend, most noticeably with Rh, is toward randomization bomb was used, and for the 500 and 1000 p.s.i.g. studies, with increasing temperature. 30 rocking autoclaves were used. In each case hydrogen Table lII.Hydr0genati0n of Propionitrile EFFECT OF TEMPERATURE 0N DISTRIBUTION ON AMINES Nitrile 1 Amine NH2) 2 Amine NH) 3 Amine N) Temp, Catalyst C.

Conv. Yield Conv. Yield Conv. Yield Conv. Yield (percent) (percent) (percent) (percent) (percent) (percent) (percent) (percent) 5% Rh/C 25 3 3 89 89 0 0 2 2 86 80 0 0 150 3 3 71 71 19 19 5% Pd/C 25 0 0 0 0 74 s4 s0 0 0 0 0 90 150 0 0 0 0 95 5% Pt/C 25 0 0 0 0 21 c7 s0 0 0 0 0 45 90 150 0 0 0 0 52 88 5% Ru/C 25 0 0 0 0 0 0 80 17-35 17-35 26 26 0 0 150 28 28 53 53 0 0 EQMPLE 4 5O reacted was determined by pressure drop. 0.1 mole of A study was made of the effect of varying the solvent, benzonit-rile in 50 m1. of hexane was hydrogenated over using a shaking bomb at 25 C. and 50 p.s.i.g. As before, 300 mg. of catalyst in each case. 0.1 mole of proprionitri'le was hydrogenated in 50 ml. Results are shown in Table V below. of hexane, the catalyst being 300 mg. of 5 percent Rh on p These results show a product quite unlike that found carbon. 50 for propionitrile. With benzonitri-le the primary amine Table V.-Distributi0n of Amine in Benzonitrile Hydrogenation Nitrile Primary amine Secondary amine Tertiary amine Pressure, Catalyst p.s.i.g.

Conv. Yield Conv. Yield Conv. Yield Conv. Yield (percent) (percent) (percent) (percent) (percent) (percent) (percent) (percent) 5% Rh/G 50 1 29 0 0 0 0 0 0 500 13 13 33 33 0 0 1, 000 1 100 33 33 68 68 0 0 5% Pd/C 50 45 50 62 68 0 0 500 55 55 49 49 0 0 1,000 55 55 52 52 0 0 5% Pt/C 50 7 18 42 110 0 0 500 5 9 60 0 0 1,000 0 0 53 122 0 0 5% RulC 50 0 0 0 0 0 0 500 0 0 0 0 0 0 1,000 0 0 1 Imine C=NH) band present.

always forms an appreciable percentage of the amines present. No tetiary amine was found atall. 'Pt produce h m econ ar m ne h re Rh a m secondary amine in the aliphatic hydrogenations. Pd is e t e orm n primary min it gave exclusively tertiary amine withpropionitrile. No ring hydrogenation was observed. -In the case of the Rh and Ru hydroe pn se n i ne wa P e e -I t will be obvious to theses-killed in the art that many modifications may he made within the scope of the present invention without departing frornthe spirit thereof, and the invention includes all suchmodifications.

Wha i cla med 1. A process for the preparation of dipropylamine by ataly ic ydroge at n o p opio h ch pro comprises contacting a solution of propionitrile in an inert solvent with hydrogen at a temperature between 0 and 80 C. and a pressure between atmospheric and 1000 References Cited in the file of this patent UNITED STATES PATENTS 2,165,515 Schmidt July 11,1939 2,166,971 Schmidt et al -July 25, 1939 2,647,146 Arthur July 28, 1953 2,690,456 Renfrew et al Sept. 28, 1954 2,784,230 Ferstandig Mar. 5, 1957 2,864,863 Young Dec. 16, 1958 OTHER REFERENCES Freifelder et al.: Jour. Am. Chem. Soc., vol. 82, page 696 (Feb. 5, 1960). 

1. A PROCESS FOR THE PREPARATION OF DIPROPYLAMINE BY CATALYTIC HYDROGENATION OF PROPIONITRILE WHICH PROCESS COMPRISES CONTACTING A SOLUTION OF PROPIONITRILE IN AN INERT SOLVENT WITH HYDROGEN AT A TEMPERATURE BETWEEN 0* AND 80*C. AND A PRESSURE BETWEEN ATMOSPHERIC AND 1000 P.S.I.G. IN THE PRESENCE OF A SUPPORTED CATALYST CONSISTING ESSENTIALLY OF FROM 0.1% TO 10% BY WEIGHT RHODIUM ON A SUPPORT, AND SEPARATING DIPROPYLAMINE AS THE SOLE SUBSTANTIAL REACTION PRODUCT. 